fixup! refactor: move repeated mock in tests to its own mock file

Author: josefinalliende

test/shared/mocks/mock_active_pubkey_notifier.dart

@@ -11,8 +11,8 @@ class MockActivePubkeyNotifier extends ActivePubkeyNotifier {
   }
 
   @override
-  Future<void> setActivePubkey(String pubkey) async {
-    pubkey = pubkey;
-    state = pubkey;
+  Future<void> setActivePubkey(String newPubkey) async {
+    pubkey = newPubkey;
+    state = newPubkey;
   }
 }